int grainTemp = thermocouple.readFahrenheit();
Serial.print("Grain Temp: ");
Serial.println(thermocouple.readFahrenheit());
Why do you need to read the thermocouple twice? Print the value in grainTemp, as the first statement implies you will.
switch(grainTemp){
case 60:
while(grainTemp >=60) {
thermocouple.readFahrenheit();
digitalWrite(acRelay, HIGH);
} //end while
} // end switch
A switch statement with one case is silly. A simple if statement would be better.
You are reading the thermocouple again, and throwing the reading away. Store it in grainTemp, so you have a ghost of a chance of the while loop ending.